Currently, a phosphorus-based flame retardant is mainly available in lieu of a halogen-based flame retardant, and examples thereof include red phosphorus, phosphoric acid ester or phosphate, phosphonate, phosphinate, phosphine oxide, phosphazene, etc.
Red phosphorus which is a compound composed exclusively of phosphorus is used to a limited extent because of the probability of generating phosphine (PH3) during processing or is being used via surface coating, which makes it difficult to show different colors and thus has limited end-uses.
Particularly useful as the flame retardant is a phosphate. According to a flame-retarding mechanism, a phosphorus-based flame retardant, which is regarded as important in terms of flame-retarding effects in solid phase, unlike a halogen-based flame retardant, has difficulty in imparting flame retardancy to styrene, acryl, and olefin polymers themselves which do not form char upon combustion, and is thus used by being blended with a polymer that facilitates the formation of char, for example, PC, PPE, phenol resin, etc.
A phosphoric acid ester-based flame retardant may be used as a plasticizer for resin, and has been initially utilized as a flame retardant and a plasticizer for polyurethane. For example, triphenylphosphate (TPP), which has begun to be widely used as a flame retardant for PC/ABS and PPO/HIPS for PPE- and PC-based blends, is further receiving attention after halogen-related problems are on the rise. However, because TPP is very highly volatile, it may volatilize during processing of flame-retarding resin, undesirably causing appearance defects due to gas clustering or carbonization. Furthermore, the volatilized gas accumulates in corners of the injection molded product, and thus may develop into cracks over time. As an alternative to TPP, resorcinol bis(diphenylphosphate) (RDP) which has improved volatility and an increased molecular weight has been employed, but is comparatively poor in terms of hydrolysis resistance. Hence, bisphenol bis(diphenylphosphate) having bisphenol in place of resorcinol as a connection chain is currently widely available because it has good hydrolysis resistance and is price competitive. However, bisphenol bis(diphenylphosphate) is problematic because it is difficult to process and is insufficiently plasticized.